A Doping Technique that Suppresses Undesirable H2 Evolution Derived from Overall Water Splitting in the Highly Selective Photocatalytic Conversion of CO2 in and by Water

Photocatalytic conversion of CO₂ to reduction products, such as CO, HCOOH, HCHO, CH₃OH, and CH₄, is one of the most attractive propositions for producing green energy by artificial photosynthesis. Herein, we found that Ga₂O₃ photocatalysts exhibit high conversion of CO₂. Doping of Zn species into Ga₂O₃ suppresses the H₂ evolution derived from overall water splitting and, consequently, Zn‐doped, Ag‐modified Ga₂O₃ exhibits higher selectivity toward CO evolution than bare, Ag‐modified Ga₂O₃. We observed stoichiometric amounts of evolved O₂ together with CO. Mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species on the photocatalyst surface, but the CO₂ introduced in the gas phase. Doping of the photocatalyst with Zn is expected to ease the adsorption of CO₂ on the catalyst surface.     

Dispersed Nickel Cobalt Oxyphosphide Nanoparticles Confined in Multichannel Hollow Carbon Fibers for Photocatalytic CO2 Reduction

Materials for high‐efficiency photocatalytic CO₂ reduction are desirable for solar‐to‐carbon fuel conversion. Herein, highly dispersed nickel cobalt oxyphosphide nanoparticles (NiCoOP NPs) were confined in multichannel hollow carbon fibers (MHCFs) to construct the NiCoOP‐NPs@MHCFs catalysts for efficient CO₂ photoreduction. The synthesis involves electrospinning, phosphidation, and carbonization steps and permits facile tuning of chemical composition. In the catalyst, the mixed metal oxyphosphide NPs with ultrasmall size and high dispersion offer abundant catalytically active sites for redox reactions. At the same time, the multichannel hollow carbon matrix with high conductivity and open ends will effectively promote mass/charge transfer, improve CO₂ adsorption, and prevent the metal oxyphosphide NPs from aggregation. The optimized hetero‐metal oxyphosphide catalyst exhibits considerable activity for photosensitized CO₂ reduction, affording a high CO evolution rate of 16.6 μmol h^?1 (per 0.1 mg of catalyst).     

利用第一性原理研究氧化铟在甲醇水蒸气重整反应中的催化作用

基于第一性原理方法,证明了甲醛在In₂O₃(110)表面可以选择性地转化为CO₂. 水分解得到的OH物种有利于甲醛脱氢得到CHO,后者不易直接脱氢,其H原子被周围的OH捕获生成CO和H₂O. 最后,相比较其从表面直接脱附,CO更容易获得一个晶格氧生成CO₂. 计算结果表明,在没有PdIn合金参与催化的甲醇水蒸气重整反应过程中,In₂O₃确实扮演着非常重要的角色,进而从理论上证实了甲醇在氧化铟表面选择性生成CO₂的实验结果.     

Cu、N共掺杂TiO2纳米管光催化重整甘油制备合成气

通过碱性水热-离子交换法制备了Cu、N共掺杂TiO₂纳米管(Cu/N-TNT),对其光催化重整甘油制备合成气性能进行了研究。结果表明,Cu/N-TNT具有富含氧空位(O_v)的管状结构,N以Ti-N形式取代部分O形成杂质能级,Cu以Cu²⁺形式掺杂在催化剂晶格间隙和表面,Cu、N共掺杂促进TiO₂表面电荷有效分离,有利于其光催化重整甘油制备合成气活性和选择性的提高。紫外光照射8h时,掺Cu量为0.15%的Cu/N-TNT催化剂上CO和H₂产量分别为7.3和8.5 mmol·g^-1,是原始TiO₂的9.1和70.8倍,n_H2/n_CO从0.52提高为1.18,n_CO/n_CO2从0.21提高至0.42。Cu/N-TNT表面N和O_V为醛类脱羰和甲酸脱水生成CO提供反应活性位点,Cu作为浅势阱提...     

Cu、N共掺杂TiO2纳米管光催化重整甘油制备合成气

通过碱性水热-离子交换法制备了Cu、N共掺杂TiO₂纳米管(Cu/N-TNT),对其光催化重整甘油制备合成气性能进行了研究。结果表明,Cu/N-TNT具有富含氧空位(O_V)的管状结构,N以Ti-N形式取代部分O形成杂质能级,Cu以Cu²⁺形式掺杂在催化剂晶格间隙和表面,Cu、N共掺杂促进TiO₂表面电荷有效分离,有利于其光催化重整甘油制备合成气活性和选择性的提高。紫外光照射8 h时,掺Cu量为0.15%的Cu/N-TNT催化剂上CO和H₂产量分别为7.3和8.5 mmol·g^-1,是原始TiO₂的9.1和70.8倍,n_H2/n_CO从0.52提高为1.18,n_CO/n_CO2从0.21提高至0.42。Cu/N-TNT表面N和O_V为醛类脱羰和甲酸脱水生成CO提供反应活性位点,Cu作为浅势阱提高光生电子-空穴分离效率。光生空穴(h⁺)是光催化重整甘油制备合成气过程中的主要活性物种,大量羟基自由基(·OH)和超氧自由基(·O₂^-)会导致甘油过度氧化,使CO选择性降低。     

Development of high performance Cu/ZnO-based catalysts for methanol synthesis and the water-gas shift reaction

Our groups studies on Cu/ZnO-based catalysts for methanol synthesis via hydrogenation of CO₂ and for the water-gas shift reaction are reviewed. Effects of ZnO contained in supported Cu-based catalysts on their activities for several reactions were investigated. The addition of ZnO to Cu-based catalyst supported on Al₂O₃, ZrO₂ or SiO₂ improved its specific activity for methanol synthesis and the reverse water-gas shift reaction, but did not improve its specific activity for methanol steam reforming and the water-gas shift reaction. Methanol synthesis from CO₂ and H₂ over Cu/ZnO-based catalysts was extensively studied under a joint research project between National Institute for Resources and Environment (NIRE; one of the former research institutes reorganized to AIST) and Research Institute of Innovative Technology for the Earth (RITE). It was suggested that methanol should be produced via the hydrogenation of CO₂, but not via the hydrogenation of CO, and that H₂O produced along with methanol should greatly suppress methanol synthesis. The Cu/ZnO-based multicomponent catalysts such as Cu/ZnO/ZrO₂/Al₂O₃ and Cu/ZnO/ZrO₂/Al₂O₃/Ga₂O₃ were highly active for methanol synthesis from CO₂ and H₂. The addition of a small amount of colloidal silica to the multicomponent catalysts greatly improved their long-term stability during methanol synthesis from CO₂ and H₂. The purity of the crude methanol produced in a bench plant was 99.9 wt% and higher than that of the crude methanol from a commercial methanol synthesis from syngas. The water-gas shift reaction over Cu/ZnO-based catalysts was also studied. The activity of Cu/ZnO/ZrO₂/Al₂O₃ catalyst for the water-gas shift reaction at 523 K was less affected by the pre-treatments such as calcination and treatment in H₂ at high temperatures than that of the Cu/ZnO/Al₂O₃ catalyst. Accordingly, the Cu/ZnO/ZrO₂/Al₂O₃ catalyst was considered to be more suitable for practical use for the water-gas shift reaction. The Cu/ZnO/ZrO₂/Al₂O₃ catalyst was also highly active for the water-gas shift reaction at 673 K. Furthermore, a two-stage reaction system composed of the first reaction zone for the water-gas shift reaction at 673 K and the second reaction zone for the reaction at 523 K was found to be more efficient than a one-stage reaction system. The addition of a small amount of colloidal silica to a Cu/ZnO-based catalyst greatly improved its long-term stability in the water-gas shift reaction in a similar manner as in methanol synthesis from CO₂ and H₂.     

Pt的氧化状态对甲醇氧化活性的影响

采用NaBH4还原法制备了XC-72碳黑负载的Pt电催化剂,并在化学还原后用H2O2处理部分催化剂以改变Pt的氧化状态,以期改善Pt活性中心上水的离解而提高催化活性.X射线光电子能谱结果表明,经H2O2处理的催化剂含有较多的氧化态Pt.通过循环伏安法和记时电流法考察了经处理和未经处理的催化剂在酸性条件下的甲醇氧化的催化...     

Site Isolation Leads to Stable Photocatalytic Reduction of CO2 over a Rhenium‐Based Catalyst

A porous organic polymer incorporating [(α‐diimine)Re(CO)₃Cl] moieties was produced and tested in the photocatalytic reduction of CO₂, with NEt₃ as a sacrificial donor. The catalyst generated both H₂ and CO, although the Re moiety was not required for H₂ generation. After an induction period, the Re‐containing porous organic polymer produced CO at a stable rate, unless soluble [(bpy)Re(CO)₃Cl] (bpy=2,2′‐bipyridine) was added. This provides the strongest evidence to date that [(α‐diimine)Re(CO)₃Cl] catalysts for photocatalytic CO₂ reduction decompose through a bimetallic pathway.     

Widely Controllable Syngas Production by a Dye‐Sensitized TiO2 Hybrid System with ReI and CoIII Catalysts under Visible‐Light Irradiation

Visible‐light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H₂ evolving Co^III catalyst and a CO‐producing Re^I catalyst on TiO₂ have been found to produce both H₂ and CO (syngas) in CO₂‐saturated N ,N ‐dimethyl formamide (DMF)/water solution containing a 0.1 m sacrificial electron donor. The H₂/CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the Re^I and Co^III catalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO₂ to each of the CO₂‐reduction and hydrogen‐evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.     

Nanoplasmonic zirconium nitride photocatalyst for direct overall water splitting

The ability of plasmonic nanostructures to efficiently harvest light energy and generate energetic hot carriers makes them promising materials for utilization in photocatalytic water spitting.Apart from the traditional Au and Ag based plasmonic photocatalysts,more recently the noble-metal-free alternative plasmonic materials have attracted ever-increasing interest.Here we report the first use of plasmonic zirconium nitride（ZrN） nanoparticles as a promising photocatalyst for water splitting.Highl...     

Study on carbon dioxide reduction with water over metal oxide photocatalysts

Various metal oxides with 0.1 wt% Ag loaded as a cocatalyst were prepared by an impregnation method and examined their photocatalytic activity for CO₂ reduction with water. Among all the prepared Ag-loaded metal oxides, Ga₂O₃, ZrO₂, Y₂O₃, MgO, and La₂O₃ showed activities for CO and H₂ productions under ultraviolet light irradiation. Thus, metal oxides involving metal cations with closed shell electronic structures such as d⁰, d¹⁰, and s⁰ had the potential for CO₂ reduction with water. In situ Fourier transform infrared measurement revealed that the photocatalytic activity and selectivity for CO production are controlled by the amount and chemical states of CO₂ adsorbed on the catalyst surface and by the surface basicity, as summarized as follows: Ag/ZrO₂ enhanced H₂ production rather than CO production due to very little CO₂ adsorption. Ag/Ga₂O₃ exhibited the highest activity for CO production, because adsorbed monodentate bicarbonate was effectively converted to bidentate formate being the reaction intermediates for CO production owing to its weak surface basicity. Ag/La₂O₃, Ag/Y₂O₃, and Ag/MgO having both weak and strong basic sites adsorbed larger amount of carbonate species including their ions and suppressed H₂ production. However, the adsorbed carbonate species were hardly converted to the bidentate formate.     

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H₂ was evaluated. Ag/AC catalysts, after reduction in H₂ at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H₂ at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H₂00 treatment displayed similar PROX of CO reaction properties to Ag/SiO₂. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.     

石墨相氮化碳的化学合成及应用

石墨相氮化碳(g-C₃N₄)具有独特的电子结构和优异的化学稳定性, 近年来不仅被作为不含金属组分的催化剂和催化剂载体, 广泛地应用于有机官能团的选择性转换、光催化分解水、氧还原和Au、Pd、Ag、Pt等贵金属的负载, 还被作为绿色储能材料和硬模板剂用于H₂、CO₂的存储和纳米金属氮(氧)化物的制备等, 在能源和材料相关领域逐渐引起人们的关注. 本文将从材料的制备和应用角度,综述国内外同行近年来在g-C₃N₄研究中所取得的一些重要进展, 并对其未来发展趋势,特别是在能源和环境领域中的应用进行了展望.     

Coupling Benzylamine Oxidation with CO2 Photoconversion to Ethanol over a Black Phosphorus and Bismuth Tungstate S-Scheme Heterojunction

Photoconversion of CO₂ and H₂O into ethanol is an ideal strategy to achieve carbon neutrality. However, the production of ethanol with high activity and selectivity is challenging owing to the less efficient reduction half-reaction involving multi-step proton-coupled electron transfer (PCET), a slow C−C coupling process, and sluggish water oxidation half-reaction. Herein, a two-dimensional/two-dimensional (2D/2D) S-scheme heterojunction consisting of black phosphorus and Bi₂WO₆ (BP/BWO) was constructed for photocatalytic CO₂ reduction coupling with benzylamine (BA) oxidation. The as-prepared BP/BWO catalyst exhibits a superior photocatalytic performance toward CO₂ reduction, with a yield of 61.3 μmol g⁻¹ h⁻¹ for ethanol (selectivity of 91 %).In situ spectroscopic studies and theoretical calculations reveal that S-scheme heterojunction can effectively promote photogenerated carrier separation via the Bi−O−P bridge to accelerate the PCET process. Meanwhile, electron-rich BP acts as the active site and plays a vital role in the process of C−C coupling. In addition, the substitution of BA oxidation for H₂O oxidation can further enhance the photocatalytic performance of CO₂ reduction to C₂H₅OH. This work opens a new horizon for exploring novel heterogeneous photocatalysts in CO₂ photoconversion to C₂H₅OH based on cooperative photoredox systems.     

An Atomic‐Scale View of CO and H2 Oxidation on a Pt/Fe3O4 Model Catalyst

Metal–support interactions are frequently invoked to explain the enhanced catalytic activity of metal nanoparticles dispersed over reducible metal oxide supports, yet the atomic‐scale mechanisms are rarely known. In this report, scanning tunneling microscopy was used to study a Pt_1‐6/Fe₃O₄ model catalyst exposed to CO, H₂, O₂, and mixtures thereof at 550 K. CO extracts lattice oxygen atoms at the cluster perimeter to form CO₂, creating large holes in the metal oxide surface. H₂ and O₂ dissociate on the metal clusters and spill over onto the support. The former creates surface hydroxy groups, which react with the support, ultimately leading to the desorption of water, while oxygen atoms react with Fe from the bulk to create new Fe₃O₄(001) islands. The presence of the Pt is crucial because it catalyzes reactions that already occur on the bare iron oxide surface, but only at higher temperatures.     

Experimental measurements and kinetic modeling of CO/H2/O2/NOx conversion at high pressure

This paper presents results from lean CO/H₂/O₂/NO_x oxidation experiments conducted at 20–100 bar and 600–900 K. The experiments were carried out in a new high‐pressure laminar flow reactor designed to conduct well‐defined experimental investigations of homogeneous gas phase chemistry at pressures and temperatures up to 100 bar and 925 K. The results have been interpreted in terms of an updated detailed chemical kinetic model, designed to operate also at high pressures. The model, describing H₂/O₂, CO/CO₂, and NO_x chemistry, is developed from a critical review of data for individual elementary reactions, with supplementary rate constants determined from ab initio CBS‐QB3 calculations. New or updated rate constants are proposed for important reactions, including OH + HO₂ ? H₂O + O₂, CO + OH ? [HOCO] ? CO₂ + H, HOCO + OH ? CO + H₂O₂, NO₂ + H₂ ? HNO₂ + H, NO₂ + HO₂ ? HONO/HNO₂ + O₂, and HNO₂(+M) ? HONO(+M). Further validation of the model performance is obtained through comparisons with flow reactor experiments from the literature on the chemical systems H₂/O₂, H₂/O₂/NO₂, and CO/H₂O/O₂ at 780–1100 K and 1–10 bar. Moreover, introduction of the reaction CO + H₂O₂ → HOCO + OH into the model yields an improved prediction, but no final resolution, to the recently debated syngas ignition delay problem compared to previous kinetic models. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 454–480, 2008     

Aqueous Electrochemical Reduction of Carbon Dioxide and Carbon Monoxide into Methanol with Cobalt Phthalocyanine

Conversion of CO₂ into valuable molecules is a field of intensive investigation with the aim of developing scalable technologies for making fuels using renewable energy sources. While electrochemical reduction into CO and formate are approaching industrial maturity, a current challenge is obtaining more reduced products like methanol. However, literature on the matter is scarce, and even more for the use of molecular catalysts. Here, we demonstrate that cobalt phthalocyanine, a well‐known catalyst for the electrochemical conversion of CO₂ to CO, can also catalyze the reaction from CO₂ or CO to methanol in aqueous electrolytes at ambient conditions of temperature and pressure. The studies identify formaldehyde as a key intermediate and an unexpected pH effect on selectivity. This paves the way for establishing a sequential process where CO₂ is first converted to CO which is subsequently used as a reactant to produce methanol. Under ideal conditions, the reaction shows a global Faradaic efficiency of 19.5 % and chemical selectivity of 7.5 %.     

Tweaking Photo CO2 Reduction by Altering Lewis Acidic Sites in Metalated-Porous Organic Polymer for Adjustable H2/CO Ratio in Syngas Production

Herein, we have specifically designed two metalated porous organic polymers ( Zn-POP and Co-POP ) for syngas (CO+H₂) production from gaseous CO₂. The variable H₂/CO ratio of syngas with the highest efficiency was produced in water medium (without an organic hole scavenger and photosensitizer) by utilizing the basic principle of Lewis acid/base chemistry. Also, we observed the formation of entirely different major products during photocatalytic CO₂ reduction and water splitting with the help of the two catalysts, where CO (145.65 μmol g⁻¹ h⁻¹) and H₂ (434.7 μmol g⁻¹ h⁻¹) production were preferentially obtained over Co-POP & Zn-POP , respectively. The higher electron density/better Lewis basic nature of Co-POP was investigated further using XPS, XANES, and NH₃-TPD studies, which considerably improve CO₂ activation capacity. Moreover, the structure–activity relationship was confirmed via in situ DRIFTS and DFT studies, which demonstrated the formation of COOH* intermediate along with the thermodynamic feasibility of CO₂ reduction over Co-POP while water splitting occurred preferentially over Zn-POP .     

Densely Packed,Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO2 Reduction

Controlling the selectivity in electrochemical CO₂ reduction is an unsolved challenge. While tin (Sn) has emerged as a promising non‐precious catalyst for CO₂ electroreduction, most Sn‐based catalysts produce formate as the major product, which is less desirable than CO in terms of separation and further use. Tin monoxide (SnO) nanoparticles supported on carbon black were synthesized and assembled and their application in CO₂ reduction was studied. Remarkably high selectivity and partial current densities for CO formation were obtained using these SnO nanoparticles compared to other Sn catalysts. The high activity is attributed to the ultra‐small size of the nanoparticles (2.6 nm), while the high selectivity is attributed to a local pH effect arising from the dense packing of nanoparticles in the conductive carbon black matrix.